1. Field of the Disclosure
The present disclosure relates to methods and apparatuses for providing integrity protection in a dual subscriber identity module (SIM) dual standby (DSDS) device.
2. Description of the Related Art
Integrity protection is present in a universal mobile telecommunications system (UMTS) or a long term evolution (LTE) system in order to confirm whether a message transmitted by a transmitter is the supposed entity, and to confirm that there is no other entity in between attempting to assume the role of the transmitter. The transmitter of the message protects the message to be transmitted by adding a message authentication code (MAC-I). The MAC-I is calculated using a Kasumi or Snow third generation (3G) scheme. An integrity key (IK), a COUNT-I, a fresh value, an encoded message, and a length of the encoded message are provided as inputs to the scheme, which assist in calculating the MAC-I. The transmitter sends the message along with the calculated MAC-I to a receiver.
The receiver of the message validates the integrity of the message by calculating the xMAC-I with the same inputs that are used by the transmitter. If the received MAC-I matches the calculated xMAC-I, the message is validated and processed further. If the received MAC-I does not match the calculated xMAC-I, the message fails for integrity and the message is discarded by the receiver.
Generally, in a DSDS device, there is a single radio frequency (RF) antenna multiplexed between two SIM stacks (i.e., SIM-1 stack and SIM-2 stack). There is always the possibility that the RF antenna is tuned away to SIM-2 stack for long durations, while the SIM-1 stack is in a connected mode with a network. For example, the SIM-2 stack may be performing an area update procedure for “n” number of seconds.
During this time, there is a black out period for the SIM-1 stack, which means the RF transceiver is not available to the SIM-1 stack. Thus, the DSDS device is more prone to miss radio resource control (RRC) signals due to frequent radio link control (RLC) re-establishment and the discarding of RLC protocol data units (PDUs) results in the discarding of RRC PDUs. There will be re-transmissions in a transmitting RRC layer for discarded RRC PDUs, however, the RRC message sequence numbers (SNs) for the retransmitted messages would have incremented. This causes a gap in the RRC message sequence number (MSN) at the receiver resulting in an RRC SN wrap around and at the transmitter, which results in a hyper frame number (HFN) increment, but the receiver still uses the previous HFN. This results in an integrity failure at the receiver leading to the discard of the message, and hence, degrading quality of service.
In conventional systems and methods, the receiver detects whether the message is the retransmission of the previous message by checking the message sequence number. This leads to wrong duplicate detection when certain signal messages are missed in between by exactly one cycle of RRC SN. In such cases, the newly received signal message will be the same message sequence number as the previously received messages RRC SN. This type of signaling miss is more prone to occur in DSDS devices, where there can be frequent RRC SN misses since the RF antenna is shared between two SIM stacks for reception.
Wrap around cases are typically only addressed when the RRC SN of a newly received message is less than the RRC SN of the last received message. Thus, the wrap around case is handled only when the signalling miss is less than one complete cycle of the RRC SN, i.e., 15 messages. For example, an RRC Rx entity the last received message may be SN 9, SN 10 to SN 1 may be missed, and then the newly received message may be SN 2. Due to the signal miss, the RRC Rx entity increments HFN by 1 in COUNT-I. This tolerance of missing 15 messages works well for a single SIM device, but for a DSDS device, it is possible to miss more than 15 RRC messages. Existing wrap around detection will not work, if the signaling miss is more than one cycle of the RRC SN, i.e., 15 messages. In this case, there will be a mismatch scenario in which the transmitting RRC entity sends the messages with HFN x+1, but RRC Rx still receives the messages with HFN x, thereby leading to an integrity failure at the RRC receiving entity. Thus, increased signaling miss is more prone to happen in DSDS devices.